This invention relates to the recovery of metal from metallic chelate complexes. More particularly, it relates to the photodegradation of metal chelates as well as the resulting photodegraded compounds using an ultraviolet light source having a wavelength no greater than 210 nm to isolate the metal portion.
There is a great need for treating chelated metals so as to be able to recover the metal portions therefrom. Currently, such chelated compounds are disposed of at landfill sites. This can cause an environmental problem and as importantly is a waste of metal when the metallic portion is an expensive metal such as nickel, copper or cobalt.
The prior art in a publication entitled "Photoredox Behavior of Transition of Metal-Ethylenediaminetetraacetate Complexes. A comparison of Some Group VIII Metals" examines the photoredox behavior of several metal-ethylenediaminetetraacetate complexes. This publication is by P. Natarajan and John F. Endicott published in the Journal of Physical Chemistry, Volume 77, No. 17, 1973. This publication states that the chromium, nickel and copper complexes are essentially inert to excitation wavelengths greater than or equal to 214 nm. In those instances where higher wavelengths have been successfully employed, an additional oxidant material has been required.
It has now been found that metallic chelates including nickel ethylenediaminetetraacetic acid (EDTA) can be photodegrated when subjected to a source of ultraviolet light having a wavelength of no greater than 210 nm. This is quite unexpected in view of the state of the art and particularly the foregoing prior art reference. Further, it has also been found that electroless nickel plating wastes can also be treated with ultraviolet light in the same wavelength parameters. The UV light breaks apart the chelating compound of a chelated nickel complex, reducing its ability to complex with the nickel and further progressively degrades the organic moieties into compounds of lower molecular weight. The freed metal can then be removed as either the oxide or the hydroxide compound.
It is an advantage of the present invention to provide a novel photodegradation method for metal chelate compounds to result in a recovery of the metallic portion.
Another advantage is a novel method for photodegrading metallic chelating compounds wherein the compounds are converted to materials of lower molecular weight.
Still another advantage is a method of the foregoing type wherein no additional chemical material is required for the effective use of the photodegrading process.
Yet another advantage is a method of the foregoing type which is economical to utilize based on electrical power requirements.
Still another advantage of this invention is a method of the foregoing type wherein the recoverable metallic product is a saleable material.